Field of the Invention
The present invention relates to a machinable zirconia, and more particularly, to a zirconia having excellent strength and fracture toughness, low hardness, and high translucency so as to have excellent machinability.
Description of the Related Art
Up to now, the field of dental restorations has been remarkably grown.
In the related art, as a material for artificial teeth substituting for natural teeth, metals have been mainly used. However, recently, prostheses made of ceramics having excellent beauty and having color similar to those of natural teeth have been widely used. As a ceramic material for dental products, zirconia has no inferiority as a substitute for metal prostheses or other ceramic materials in terms of strength and beauty. The zirconia has chemical resistance, abrasion resistance, and a high melting point. Therefore, the zirconia is a material which has attracted much attention in various industrial fields beside the dental field. In addition, since the zirconia is a material which is free from cytotoxicity, carcinogens, heavy metals, and the like, the zirconia has been favored as a ceramic for biological structures.
Recently, a prosthesis is manufactured by using the zirconia in a CAD/CAM manufacturing method (design and manufacturing method utilizing a computer) instead of a prosthesis manufacturing method of the related art. In the CAD/CAM manufacturing method, after a state of the mouth is directly scanned, or a mold for manufacturing a prosthesis is scanned without a process of casting a dental mold as a general process, a form of teeth is designed by using a CAD program, and the prosthesis is manufactured. Based on virtual teeth completed by using the CAD program on a computer, the zirconia is machined by a dedicated milling machine, so that actual teeth suitable for a patient are completed.
However, the zirconia used as a material for dental products has a disadvantage in that machining is hard to perform because of high hardness although mechanical properties are excellent. Because of this problem, before a sintered body is finally completed, a porous zirconia is manufactured through primary sintering at a low temperature, and after that, a machining step is performed, and secondary sintering is performed, so that the prosthesis is completed. By taking into consideration shrinkage of the porous zirconia during the final sintering process, the prosthesis needs to be formed with a volume which is larger about 20% or more.
As described above, since the zirconia has a problem in that the machinability is deteriorated, much time and cost are spent on manufacturing the prostheses for artificial teeth. In addition, since it is difficult to machine the final shape of the prostheses as an optimized structure for the patient's mouth, there is a limitation to increase competitiveness of the zirconia prostheses.